1. Field of the Invention
This invention relates to a video-signal transmitting and a video-signal receiving apparatus for use in a video-signal transmitting and receiving system which subjects a video signal, such as a television signal, to digital high-efficient coding for transmission and reception.
2. Description of the Related Art
A system which subjects a high-resolution television signal (hereinafter, referred to as a high-resolution TV signal) to high-efficient coding, transfers the coded signal, and causes a receiver to decode the transmitted signal are known. The high-resolution TV signal is supplied to a high-efficient coding circuit of an HDTV (high-definition television) encoder. The HDTV encoder is composed of a high-efficient coding circuit and an output buffer. The high-efficient coding circuit subjects the signal supplied from the input terminal to high-efficient coding and supplies the coded signal to the buffer. The output buffer is a smoothing buffer for outputting a transmitted signal at a constant transmission rate to a transmission line. The output buffer, when the amount of signals stored exceeds a specified value, feeds back a control signal to the high-efficient coding circuit in order to reduce the amount of signals supplied from the encoding circuit. The constant-rate signal supplied from the HDTV is supplied to an input buffer of an HDTV decoder via the transmission line. The HDTV decoder is composed of an input buffer and a decoding circuit. The input buffer stores the signals supplied from the transmission line and supplies a constant-rate signal to the decoding circuit. After the signal supplied to the decoding circuit has been decoded, this decoded signal is supplied to an HDTV monitor for display.
In the above-described, the high-resolution TV signal supplied via the input terminal is subjected to high-efficient coding at the HDTV encoder, and then is supplied to the HDTV decoder via the transmission line. The HDTV decoder decodes the signal supplied via the transmission line, and then displays the decoded signal on the HDTV monitor.
With this system, when a low-resolution TV signal is transmitted, the low-resolution signal is converted into a high-resolution TV signal and then the converted signal is transmitted on the same transmission line. When the display unit of the receiver can only make a low-resolution display, the high-resolution TV signal transmitted must be decoded by the HDTV decoder, and then the decoded signal must be converted into a low-resolution signal (i.e., down converted).
As described above, with a conventional system for subjecting a high-resolution TV signal to digital high-efficient coding before transmission, only a high-resolution TV signal can be transmitted. Because of this, to make use of existing television software, a low-resolution TV signal must be converted into a high-resolution TV signal on the transmission side. When the display unit of the receiver can only provide a low-resolution display, the received high-resolution TV signal must be decoded the decoded signal converted into a low-resolution signal.